A cellular radio access network (RAN) is a radio network comprising a number of cells. Each cell is served by a transceiver, such as a Base Station (BS) in a Global System for Mobile Communications (GSM) network or a NodeB in an Universal Mobile Telecommunications System (UMTS)/Wideband Code Division Multiple Access (WCDMA) network. The BSs and NodeB are further controlled by RAN controller nodes. A Base Station Controller (BSC) is a RAN controller node in a GSM network or more precisely in the GSM EDGE Radio Access Network (GERAN), and a Radio Network Controller (RNC) is a RAN controller in a UMTS network or more precisely in the Universal Terrestrial Radio Access Network (UTRAN). The cellular system is used in order to provide connectivity to subscribers of the service in a wider geographic area than could be covered by a single BS.
A Mobile Switching Centre (MSC) is a communication switch or exchange in the communication network. The MSC provides circuit switched telephony, mobility management and supplementary services to both GSM and UMTS subscribers with mobile phones roaming within the area that it serves. An MSC may serve a number of cells within the cellular network. The cells in a cellular network are further divided into Location Areas (LA) in the circuit switched domain. Each cell belongs to one LA only in the traditional GSM and UMTS networks. Additionally, one LA can only be controlled by a single MSC and this “building of logic” means that a LA can be used to uniquely identify the MSC (or pool of MSCs) that is controlling the group of cells belonging to one LA. However, one MSC may control more than one LA. A Location Area Identity (LAI) is used to identify a LA. A LAI consists of a Mobile Country Code (MCC), a Mobile Network Code (MNC) and a Location Area Code (LAC). A similar concept to LA but in the packet switched domain is the Routing Area (RA). Cells are identified in a different way in GSM and UMTS networks. In GSM networks, the cell identifier is called Cell Global Identifier (CGI) and the CGI consists of the LAI (as defined above) and a Cell Identifier (CI). In UMTS networks, the cell identifier consists of RNC-Identity (RNC-ID) and a cell identity.
When a mobile user moves between cells in a network, a handover is initiated to hand the user over from one cell to another. The handover is controlled by the RAN Controller and the decision to perform handover in the RAN Controller is based on e.g. measurement reports received from the user equipment (UE)/mobile station (MS). The network informs the UE about the neighbouring cells and the UE measures the signal strength received from these cells and reports the measurements to the RAN Controller. On some occasions, a handover will be required where the source cell and the target cell are both controlled by the same MSC. Handover between cells controlled by the same MSC is called Intra-MSC handover. On other occasions, a handover will be required in which a user will be handed over from a cell served by one MSC to a cell served by another MSC. This handover between MSCs is called Inter-MSC handover.
Referring to FIG. 1, there is illustrated schematically the architecture and principle of inter-MSC Handover. A terminal 1 is located inside one of the Location Areas (LA1) served by MSC1 (i.e. one MSC can control more than one Location Area, but only one is shown in FIG. 1). If the terminal 1 is in a Circuit Switched (CS) dedicated state, that is to say it is involved in on or more CS sessions, then Intra-MSC handovers are performed as required within LA1 as long as the terminal remains within LA1.
If the terminal 1 moves to area LA2, which is served by MSC2, then an Inter-MSC handover needs to be triggered from MSC1 to MSC2 to ensure that MSC2 becomes aware that the terminal 1 is about to move to LA2 from LA1. As described above, the handover is triggered from the RAN controller of the current cell in LA1 (also called the source cell). The RAN controller of the source cell selects the target cell and signals the need to trigger handover towards MSC1. This request contains the cell identifier of the selected target cell (e.g. a CGI for GSM cells or RNC-ID and Cell Identifier for UMTS cells). The main steps of the handover are based on the make-before-break principle which means that the needed radio resources are reserved for the UE in the target cell before the UE moves there. The main reason for this is to minimize any noticeable interrupt time for the circuit switched service during handover.
In order to find MSC2, MSC1 consults a mapping table that maps the target cell or node identity received from the RAN controller to the address of MSC2. This is termed herein ‘handover routing’. In general, handover routing means that the source MSC (in this case MSC1) selects the target MSC (in this case MSC2) based on the received target cell or node identity, and initiates the signalling required for the handover towards the target MSC. Once the target MSC receives the indication about the handover request, it uses the received target cell or node information to decide which RAN controller is controlling the target cell.
The target cell or RAN controller node is identified for example by:                A Cell Global Identifier (CGI) or any parts of the CGI for GERAN/GSM cells; and        A Radio Network Controller identity (RNC-ID) for UTRAN/WCDMA cells.        
The Handover Routing tables are logically built and used as follows:    1. The Handover target cell or target node provides the name of the target MSC that controls the target cell;    2. The target MSC name is used to obtain a signalling number 7 Destination Point Code to be used in the underlying Message Transfer Part (MTP) used for the handover.
FIG. 2 is a combination of FIGS. 5a and 6a from 3GPP TS 29.010 v6.9.0, and is a signalling diagram showing Basic Inter-MSC handover from a GERAN/GSM cell to another GERAN/GSM cell. Previously, there has only been a limited need to define MSCs in a Core Network, and only so-called ‘neighbouring’ MSCs (MSCs that are controlling cells in adjacent/overlapping locations) are defined. This is because handover normally occurs only in the case of a user moving from one geographic location served by one cell to a new geographic location that may be served better by another cell.
FIG. 3 illustrates further which LAs are covered by which MSCs. The handover tables held at each MSC defines adjacent MSCs. For example, the Handover Routing Table of MSC1 defines MSC2, MSC7 and MSC8, as these MSCs control cells that are adjacent to some of the cells controlled by MSC1, and therefore may be a possible target for an Inter-MSC handover from MSC1. Similarly, MSC1 is defined in the Handover Routing Tables of MSC2, MSC7 and MSC8, as MSC1 is a possible target for Inter-MSC Handover from any of MSC2, MSC7 and MSC8. The Handover Routing Table of MSC8 would need to define MSC1, MSC2, MSC3, MSC7, MSC9, MSC13, MSC14 and MSC15, as each of these are a possible target for an inter-MSC Handover from MSC8. However, the Handover Routing Table of MSC-16 does not define MSC1, since there are no neighbouring cells controlled by MSC1 to which a mobile subscriber might require handover.
This solution has worked well so far with existing GSM and WCDMAA/JMTS networks. However, there are new network scenarios and node types being developed that were not envisaged when designing Handover Routing. Examples of some new network scenarios include:    Circuit Switched over Long Term Evolution (CSoLTE) solutions where one or few Packet Mobile Switching Centres (PMSCs) could serve a whole country. A PMSC may serve both traditional 2 G/GSM and 3 G/WCDMA/UMTS radio access networks and the networks based on Circuit Switched over Long Term Evolution-capable networks.    Generic Access Network (GAN) access in different Public Land Mobile Networks (PLMNs)    Where a PLMN is purchased and it is necessary to provide Handover between the existing and new PLMNs (i.e. the existing and new PLMNs provide coverage on the same geographical area).
These new network scenarios require that all MSCs in a network will need to define all other MSCs in a network, and not simply MSCs that serve adjoining cells. In other words, Handover Routing for these new network scenarios require a full-mesh configurations in both directions (e.g. from MSC1 to MSC18 and from MSC18 to MSC1).
There are several problems with the full-mesh configuration, the main two being that it requires each MSC in a network to configure and store a large amount of data. Furthermore, it may require sharing data about MSCs in a network with MSCs in another network. Where these networks are operated by different network operators, these network operators may not wish to share all of the information required, some of which may be confidential.